The present invention generally relates to the processing of materials, and more specifically processing substrates for electronics, optics or optoelectronics. In particular, the invention relates to a high-precision automatic cutting device for cutting an assembly that includes a layer of material having a weakened zone which is attached to a source substrate. The device includes cutting means and holding means.
The invention also relates to a high-precision automatic cutting method, wherein an assembly that includes a layer of material attached to a source substrate is detached via a weakened zone. The method includes holding the assembly with a holding means, and cutting the assembly to detach the layer from the source substrate with a cutting means. It should be noted that the invention is particularly suitable for cutting layers having a thickness less than approximately one hundred microns, and in particular for cutting “thin” or useful layers, having a thickness on the order of one micron.
It should be noted that the term “cutting” when used herein means dividing a single item or assembly into two distinct parts such that the parts are not joined again. As discussed below, such cutting within the scope of the invention is conducted on a weakened zone.
Devices and methods are used to form layers (thin or not), which may be transferred from the source substrate to a “target” substrate. The substrates generally come in the form of disks generally referred to in the field as “wafers”. The wafers may be made of a semi-conductor material such as silicon.
A person skilled in the art knows how to form a weakened zone inside a wafer along a plane that is parallel to the main faces of the wafer. For example, the weakened zone may be produced by implanting ions through the surface of the wafer. The ions create a weakened layer in the volume of the wafer that delimits a lower region (which corresponds within the scope of this text to the source substrate) and an upper region adjacent to the ion source (which corresponds to the layer to be cut). An example of such a method used to produce thin layers is found in U.S. Pat. No. 5,374,564.
It is also possible to produce the weakened zone by other known means, for example, by constructing an intermediate region of porous material between two regions of dense material. An embedded oxide layer could be formed in a substrate (e.g. an Silicon On Insulator (SOI) type substrate) or by adhering two layers together, wherein the adhesion zone corresponds to the weakened zone.
It should also be noted that it is possible to process SOA (Silicon On Anything) type substrates or even AOA (Anything On Anything) type substrates in this manner. Thus, the cutting of such substrates falls within the scope of the invention.
To implement cutting along the weakened zone and to thus divide the source substrate and the layer of material into two distinct parts, it is possible to use a manual operator. However, using a manual operator limits the layer production output. In addition, such operations may not be reproducible. Automatic cutting devices and methods aiming to do away with the abovementioned drawbacks are known. An example of such a device and method is disclosed in U.S. Pat. No. 6,418,999. The device according to this patent uses a water jet to impact a slice of a wafer which is held on its two main faces, wherein the water jet engages a weakened zone and divides the wafer into two parts. This device includes holding means associated with the two respective faces of the wafer, and the holding means enables a certain predetermined separation to occur between the two parts of the wafer during cutting.
It is important to manage the separation between the two parts of the wafer located on either side of the weakened zone with precision, particularly when these two parts are made of different materials. For example, when cutting an assembly including a layer of silicon attached to an SiC substrate via a weakened zone, the silicon layer undergoes significant deformation (the SiC substrate being considerably more rigid and undergoing considerably less deformation), which may cause damage to the silicon layer.
The device disclosed in U.S. Pat. No. 6,418,999 attempts to provide a solution to accompany separation and/or deformation of the two parts of the wafer in the desired manner. However, one restriction associated with this device is that it includes only passive means to enable a specific separation and/or a specific deformation. The passive means correspond to specific configurations of the holding means, wherein the surface may include cavities of given geometries to enable a specific spacing between the parts of the wafer. It is also possible, according to this document, to give the surface of the holding means a generally convex shape, or to provide a layer of elastic material on the surface of the holding means which contacts the wafer. But such passive solutions cannot be used to accompany the separation or spacing apart and/or deformation of the parts of the wafer because there is no actual control (i.e. control in active mode) carried out by the device disclosed in U.S. Pat. No. 6,418,999. In addition, it should be noted that the holding means must also rotate the wafer so that the entire periphery of the wafer is engaged by a water jet, which complicates the design and operation of the device.